Air pollution has been a serious problem all over the world. Engine exhaust either resulted from industries or motor vehicles constitutes the chief source of air pollution. The worst pollutants including carbon monoxide, hydrocarbons, nitrogen oxides and sulfur oxides ect. have known to all, and various means have been devised to eliminates them from forming killing smogs. The abovementioned chemical compounds floating in the air can interact with sun and form photochemical smog which is also bad to health. Besides, engine exhaust gives noise.
Those devices so far provided could seldom give a cure all result and usually the costs are high.